Data security is an important aspect in multimedia commerce. Conditional access systems (CAS) mainly rely on scrambling of a transport stream containing protected multimedia contents. In Digital Video Broadcast (“DVB”), for example, only subscribers with a conditional access module (“CAM”) and a valid subscriber card (Smart Card “SC”) can descramble a scrambled transport stream and obtain TV contents in the clear for application to a TV set. The conditional access module must have the capability to process an MPEG stream in real-time at a processing rate of at least about 1.5 MB/sec, thereby placing high demands of performance on the hardware used in the CAM.